1. Field of the Invention
This invention relates to a recording medium for a printer having a dye fixing layer containing an interlayer compound and a binder, wherein the interlayer compound fixes and holds a water-soluble dye by an intercalation reaction which is based on an intercalation reaction. More particularly, it relates to an improvement in a binder used for the dye fixing layer.
2. Description of the Related Art
Among the methods for outputting the picture information or letter code information, formulated by a personal computer or a word processor, on a recording medium for a printer, such as an overhead projector, referred to below as an OHP sheet, there is known an ink jet recording method in which an ink containing a water-soluble dye is emitted to the recording medium for the printer via a recording nozzle operating under electrolysis or thermal pressure as a driving source to form an image on the recording medium for the printer.
This ink jet recording system is recently finding increasing use in homes and in offices because it has many advantages, such that the recording noise is small, running costs are low, an image can be formed on ordinary paper sheets and no waste materials, such as ink ribbons, are produced.
Meanwhile, the water-soluble dye, used in such ink jet recording system, is usually held by the reciprocal action, such as Van del Val""s force with the dye fixing layer constituting portion, or by the hydrogen bond, after the water-soluble dye is transferred to the dye fixing layer of the recording medium for the printer. Therefore, if, after image formation, a solvent exhibiting higher affinity to the dye, such as water, is contacted with the image, this solvent is dissolved from the dye fixing layer to blur the image. Moreover, if the thermal energy or water steam sufficient to cancel the Van del Val""s force between the water-soluble dye constituting the image and the dye fixing layer constituting portion or the hydrogen bond is supplied to the recording medium for the printer, the water-soluble dye is migrated to blur the produced image. In addition, if the water-soluble dye constituting the image is exposed to the high energy light rays, such as ultra-violet rays, the image tends to be faded or changed in color or lowered in the gray level of the image due to decomposition of the dye itself.
For improving the fixation, for example, water-proofness, of an image in such ink jet recording system, there is proposed a recording medium for the printer in which the dye is fixed and held on the dye fixation layer by an intercalation reaction which is based on the ion exchange operation. Specifically, there is proposed in Japanese Laying-Open Patent H-7-69725 a recording medium for a printer having a dye fixation layer containing an interlayer compound for fixing and holding the dye by the intercalation reaction and a hydrophilic binder resin, such as a polyvinyl pyrrolidone resin, a polyvinyl butyral resin, a hydroxy propyl cellulose resin or a polyvinyl alcohol resin.
However, this recording medium for the printer, while being improved in ink fixation and resistance to color fading or color change on storage or to lowering of the gray level, is not optimum in ink absorption or water-proofness. In particular, in a portion of the recording medium for the printer where there are deposited ink liquid droplets to high density, the ink liquid droplets are mixed together before being absorbed in the dye reception layer of the recording medium for the printer to deteriorate the image resolution.
It is therefore an object of the present invention to provide a recording medium for the printer having a dye fixation layer mainly composed of an interlayer compound for fixing and holding the water-soluble dye by an intercalation reaction and a binder, in which the ink is improved in absorption, fixation, water-proofness and anti-bleeding characteristics to enable an image to be formed to high resolution.
The present inventors have conducted perseverant researches towards accomplishing the above object, and have found that if, in a recording medium for the printer having a dye fixation layer mainly composed of an interlayer compound for fixing and holding the water-soluble dye by an intercalation reaction and a binder for the dye fixation layer, a urethanated polyvinyl alcohol resin, urethanated in a pre-set proportion is used as the binder of the dye fixing layer, a clear image can be held which is free from color bleeding. This finding has led to completion of the present invention.
In one aspect, the present invention provides a recording medium for a printer in which a dye fixation layer mainly composed of an interlayer compound and a binder is formed as an outermost layer on a substrate, in which the interlayer compound fixes and holds a water soluble dye by an intercalation reaction derived from an ion exchange action. The binder for the dye fixation layer contains urethanated polyvinyl alcohol resin, with the urethanation ratio of the urethanated polyvinyl alcohol resin being 1 to 20 mol %.
In another aspect, the present invention provides a recording medium for a printer in which a dye fixation layer mainly composed of an interlayer compound and a binder and at least one ink absorption layer containing an ink absorbing resin are formed sequentially on s substrate. The interlayer compound fixes and holds a water soluble dye by an intercalation reaction derived from an ion exchange action. The binder for the dye fixation layer is a urethanated polyvinyl alcohol resin having an urethanation ratio of 1 mol % to 50 mol %.
The recording medium for the printer according to the present invention uses a material containing an urethanated polyvinyl alcohol resin as a binder, with the urethanation ratio of the urethanated polyvinyl alcohol resin being set to a pre-set range, so that the ink absorption, fixation and water-proofness and the image bleeding characteristics are improved to assure the formation of a high resolution image. Meanwhile, in the recording medium for the printer according to the present invention, an optimum value of the urethanation ratio differs depending on whether or not there is the ink absorption layer on the dye fixation layer, as mentioned above. However, the above characteristics are improved in either cases.
The recording medium for the printer according to the present invention uses, as a binder, a material containing an urethanated polyvinyl alcohol resin, having the urethanation ratio set to a pre-set range, so that the ink absorption, fixation and water-proofness and the image bleeding characteristics are improved to assure the formation of a high-resolution high-quality image.